Overload protection mechanism



I`Iuly 5, 1949. E. M. cALKlNs OVERLOAD PROTECTION MECHANISM Filed Feb. 14, 1946 275 iff ITE,

Patented July 5, 1949 UNITED STATES PATENT OFFICE 3 Claims.

The present invention relates to overload protection mechanism for use in electric circuits which mechanism includes a fuse for protection against short circuits and a resettable thermal controlled arrangement for opening the circuit against overload or snea currents which although not strong enough to blow the fuse will if long continued cause injury to the apparatus connected with the line.

An object of the present invention is to provide an overload protection mechanism having non-disruptable separable parts for opening an electric circuit when the current in the line approaches a dangerous value.

Another object of the present invention is to provide mechanism operated by an increase in temperature above a predetermined value, to open an electric circuit, and which means is capable of being reset after the temperature drops.

A still further object of the present invention is to provide an improved universally applicable replacement mechanism suitable for use in existing types of explosion fuses and which can be reset after being opened, as it contains no part which is disrupted by overload conditions.

The invention has for an additional object the provision of an overload protection mechanism in which two contacts are normally retained in circuit relation by latch means, the latch means including a bimetal hook member subj ected to the iniiuence of heat generated by flow of current through the mechanism and operable on the occurrence of a temperature above a predetermined value to unlatch said contacts for separation thereof to provide a gap in the circuit.

Another and yet further object of the present invention is to provide an overload protection mechanism wherein a heating coil is provided for separating two latched parts to open an electric circuit on occurrence of a predetermined value current iiow not in itself suiiicient to blow the fuse.

A still further object of the present invention is to provide an overload protection mechanism having latch means normally engaged to hold the circuit closed and having a heating coil effective to separate said latch means on occurrence of line current beyond which continued safe operation is not assured.

A still further object of the present invention is to provide an overload protection mechanism having a contact carrying drop-out member normally held by latch means in circuit-closing relation and which is unlatched by means subjected to the influence of heat generated by the now of.

current through the mechanism, said member being relatchable after temperature drop to close the circuit through the mechanism.

Another and still further object of the present invention is to provide an overload protection mechanism having reusable or resettable circuit opening means to interrupt or open a circuit when an excess current flows through it.

A still further object of the present invention is to provide an overload protection mechanism having relatively movable line contacts normally held in circuit closing relation by latch means, and means subjected to the inuence of heat generated by the flow of current through the mechanism operable on the occurrence of a temperature above a predetermined value to unlatch said contacts for separation thereof to open the circuit, said line contacts being returnable to circuit closing relation when the line temperature has dropped so that the contacts may again be in operative relationship.

The above, other and further objects of the present invention will be apparent from the following description and accompanying drawing.

An embodiment of the present invention is i1- lustrated in the accompanying drawing and the views thereof are as follows:

Figure 1 is a view, partially in section and partially in elevation, of an explosion-type fuse utilizing an overload protection mechanism which includes the principal features of the present invention;

Figure 2 is a vertical sectional view through the mechanism of the present invention; and

Figure 3 is a fragmental elevational view of a part of the mechanism of the present invention, showing the short circuit blow-out fuse.

As shown on the drawing:

An explosion fuse structure is illustrated including a main tube or cartridge 5 of iiber or other suitable insulating material, which is threaded at its upper end to threadingly engage a metallic contact member or ferrule 6. The upper neck 1 of the member 6 is threaded to receive internal threads on a cap 8. The ferrule 6 and cap 8 are made of a conducting material, as the member 6 is adapted to engage a suitable clip or other mechanism for connecting the cartridge in circuit. Surrounding the lower end of the cartridge 5 is a ferrule 9 adapted to engage another clip or other contact member for completing a circuit.

The overload protection structure or refill unit designated generally as A, is positioned within the cartridge 5.

The structure A is shown as comprising a casing which may be formed in two parts, Figure 2 showing an upper part I and a lower part II, arranged with the upper end of the lower part I I overlapping the lower end of the upper part I0. The casing is made of insulating material, such as ber or the like. The upper end of the casing is closed by a cap I2 of metal or other suitable conducting material which, when the fuse link structurefxA.. isfinstalled in the cartridge 5, is clampedfbetween'the upper margin of the ferrule 5 and the cap 8 to establish electric contact between the ferrule and the cap I2. As shown, disposed near the lower end of the upper part I0 of the casing is a *collar I3,- ofinsulating material, having a central openingl III therein serving as a guide for a drop-out member such as a plunger I5 movable into and out' of the lower open end of the casing.

Loosely mounted on. pins I6 and I'I, near the lower part of the casing, is aV stationary contact 18. y"The'Contact'maybe mounted 'on' the pins `so "as tdmove along them,"and`"may be constrained away from the inn'er"`surface` of the casing by a spring lI Swhich serves also to maintain' electrical "engagement/between thecontacts I8 and 2U.

lthough-"the Contact' I S'has been mentioned 'as stationary, yetit 'may"be"mov`able, to a slight extent on the"pins,"`the word stationary being "used "to signify :that 'the Contact 'remains staticna-ryas fai as displacement.' from the casing is concerned.

Theplllnger""I5'is provdedwith a 'contact 2G to engage the stationary contact I8 'inY circuit closing relation.

"Thef'plunger "or"drop-out 'member l5 would dropr out of 'the`ca`sing unless prevented or re- "strained,

' The illustrated` form ofi restraining means in- A 'cludes cooperating latchingparts. 'The upper end' ofthe plunger`15 "may beformed'with'an annular groove 2I underneatha head portion 22, "the head"p`o'rtion isshown'as of frusto-conical formtoguide the upper end of`fthe plunger into thef guide `I3"when the'plunger isapplied to the casing; asw'ill` be more fully explained.

" Attached" to' the cap I 2 is" a bim'etallic istrip or element 23 having ah'ook"`2lt 'atits 'lower end to `'enge'.ge underne'atl'll the'head 2210i' the plunger jI 5 when 'theplung'er I 5 has been moved into the "casing, through 'itsop'enlower end, to establish 'circuit-'making relationship between the contacts I8 and 20.

Between the head I2and `the stationary contact'|8 isla'conductor' 25havin'g a h'eating'coil 26 formed `in it,'adjacent the 'cap I2, and surroundfing `the" ibim'etallic n"element l 23. The conductor continuesl downwardly through" the guide' collar I3 where it is electrically'connected 'to-the stationary lcontactl I8. The conductor 25 is'bent or otherwisearrranged'as 'to be out `of the' path of movement of thehook 24.

I'Carried by'the 1plunger I5 and inl electrical fconnectionhwithlthe' contact 20 is a conductor 21 lterminatinglfin a'termin'alf28. Theterminal 23 ibis':mountedonthe-plungerv I5 as maybe observed 'IinElgures liandlS. VCarried bythe lower end of the-fplungen I5is"'af pig tailc'onductora an end 'of whichhis electrically? connectedv to theferrule i"fi'by-fmeans" of alsuitab'le set screw? 30. `'Between fthe 'fpightail 23.l and thelconductorf'Z'I is a weak flink'. or:.'.sho`rtf'circuit'blow-outr fuse 3 I calibrated to blow underv short circuit. A binding posi; 36 `:connects the pigA tail 29 to the link 3| and circuit through the mechanism.

.Theicollar I3rinadditionto' serving' as afguide for the upper end of the plunger I5 when it is inserted in the casing may be useful to maintain the plunger substantially centrally of the casing when the plunger is latched so that its contact 20 is in electrical engagement with the contact I8.

For moving the plunger I5 downwardly, when the latch means are disengaged, I preferably utilize a spring 32 attached at its upper end as by a screw 33 to the plunger I5 and hooked at its lower end 34'over the margin of the lower open end of the casing. The spring 32 is tensioned when the plunger is in latched engagement with the hook 24 so that as Soon as the latched engagement is disturbed the plunger is pulled downwardlybythe spring thus separating the electric connection between the contacts It and 2Q and dropping 'the plunger out of the casing.

Thecasing is provided with an opening 35 adjacent the hook 24 of the bimetal element 23 so that a tool may loe inserted to disengage the hoolf. 24 from the head 22 of the plunger I 5 in the event it is desired to inspect `the contact 23s The bimetal element 23 and the heating coil 25 are sodesigned" that the hoolr end Erl oi the bimetal elementwill `be removed from underneath the head22 of the plunger I5 when' the temperature in the 'zone 'of the heating coil 25 reaches a predetermined value whereupon the hook will become disengaged from the head 22 and the springZ'will yank the plunger down and out of the'lower end of Vthe casing thus openlng the circuit betweenv the contact engaging upper ierrule E andI the contact engaging the lov/er errule 3 of the cartridge 5.

The `lowerpartl I I'of the casing constitutes an arc shoot.

' In ordertov 'reset the overload protection strucf ture after "it hasbeen once' opened all that is necessary'to bedone'isy for an attendant to enter the plunger 'I 5 through the lower end of the casing and raise it through the` guide collar l 3 until its `head 22 snaps over thehook 24 of the bimetal element. VBecause 'of the opening of the circuit the temperature in theheating coil 2tY drops and Uwhen these build'up the temperature to a point which, if'it increased;"m`ight cause damage to the apparatus'connectedV to the line, the bimetal element 23 moves to' unlatch'the plunger I5 for its 'withdrawal fromthe tube and opening of the 'circuit in which the link. lstructure-is installed.

It'will be observed that the overload protection structure of the present invention is one which may be manufactured at economical cost, is one in which the plunger and bimetal element maybe relatched or reset whenever unlatched, without the replacementof some disrupted part, such as a fusible element. 65'

Of course, when the blow-out fuse l3I blows it has to be replaced, however the number of times the fuse link structure would function to open the circuit-because of overload "is greater than the number of times that the fuse 3| would blow under short' circuitv conditions. It may be understood that the structure of the present invention is' a handy one and may be readily reset simply' by returning the plunger I5 into the casing' and 'raising it until its upper endhooks'with the end 'of the bimetal element Z3 'whereupon' 'the' 'structure `is' ready for further use.

The relationship of the bimetal element 23 and the heating coil 26 determines the maximum capacity of the fuse link structure. Thus having constructed such a structure with a known capacity the structure may continue in use without any fear of burning out any of the equipment connected to the line as it is assured the circuit will open when the maximum capacity of the structure is reached, that is to say when the temperature of the heat generated in the heating coil 20 by the ilow of sneak currents through it rises to the value where the hook end 24 of the bimetallic element is moved away from latched engagement with the head 22 of the plunger I5.

By dangerous value, used in connection with the temperature created by sneak or other overload currents, is meant any temperature beyond which the continued safe operation of apparatus connected in the line is not assured.

It will, of course, be understood that various details of construction may be varied through a wide range without departing from the principles of this invention and it is, therefore, notl the purpose to limit the patent granted hereon otherwise than necessitated by the scope of the appended claims.

I claim as my invention:

1. An overload protection structure comprising a casing open at one end and closed at the other end, a plunger movable into and out 0i said casing through said open end, hook means ior engaging said plunger to hold it in the casing, a first contact mounted within the casing, a second contact mounted on the plunger and in circuit closing engagement with said rst contact when said plunger is engaged by said hook means, a conductor connected to said first contact, a second conductor connected to said second contact, a heating coil in said first conductor, said hook means comprising a bimetal element through said coil subjected to rise of temperature in said coil to become disengaged from said plunger, spring means for withdrawing said plunger when so disengaged, said spring means being attached at its upper end to a side of said plunger and removably engageable at its lower end over the lower edge of said casing to bias said plunger downwardly and a fusible link on said plunger in the circuit to said second contact for opening the circuit under short circuit conditions.

2. In combination with an explosion fuse cartridge having a separable ferrule at its upper end and a ring ferrule adjacent its lower end, an overload protection device comprising a tubular structure having a contact member at its upper end for electrical connection with the upper ferrule of the cartridge and open at its lower end, a contact member `within said tubular structure mounted and guided for movement radially of said structure, a conductor joining said contact members in circuit relation, a drop-out plunger within said structure and movable axially thereof into and out of said structure through said open lower end, a contact member on said plunger engageable with said second mentioned contact member when said plunger is in place within said structure, means for latching said plunger in place in said structure, means within said structure encompassing the upper end of said plunger to guide it into latching position, resilient means for ejecting said plunger from the tube of said structure when said latching means are released, said resilient ejecting means being disposed between said structure and the side of said plunger for fixed attachment to the side of said plunger and releasable attachment to the open lower end of said structure a conductor on said plunger including a pig tail connected to the ring ferrule on said cartridge to thereby electrically connect said first contact and said ierrule when said plunger is latched in place.

3. In combination with an explosion fuse cartridge having a separable ferrule at its upper end and a ring ferrule about the cartridge adjacent its lower end, an overload protection mechanism comprising a tubular structure having a contact member at its upper end for clamping engagement with the separable ferrule at the upper end of said cartridge and open at its lower end, a contact member within said structure mounted and guided for movement radially oi said structure, a spring acting against said contact to urge it away from said tubular structure, a conductor joining said contact members in circuit relation, a drop-out plunger within said structure and movable axially thereof into and out of said structure through said lower open end, said plunger having a head at its upper end, a contact member on said plunger engageable with said second mentioned contact member when said plunger is in place within said structure, a hook engageahle with the head of said plunger for latching said plunger in said structure with its contact against said second mentioned contact, a collar within said structure encompassing the upper end of said plunger to guide it into latching position, a spring connected between said plunger and tube for ejecting the plunger from the tube when said latching means are released, the conductor between said rst and second contact members being coiled and constituting a heating coil, a bimetal member secured at one end to said first contact and supporting said hook at its other end and projecting through the coil in said rst conductor, a conductor electrically connected with the contact member on said plunger and to the ring ferrule on said cartridge to thereby electrically connect said rst contact member and said ferrule when said plunger is latched in place, and a fusible member in said last mentioned conductor adapted to blow under short circuit condition.

EUGENE M. CALKINS.

REFERENCES CITED The following referenlces are of record in the le of this patent:

UNITED STATES PATENTS 

